This invention relates to electro-mechanical probes which are used in testing microscopic circuits such as those which are in semiconductor chips and multichip interconnect modules.
During the fabrication of semiconductor chips, it is necessary to probe and test the chips individually before they are soldered or otherwise permanently placed in a multichip interconnect module. Similarly, it is necessary that the bare multichip interconnect module (such as that described in U.S Pat. No. 4,721,831) be probed and tested before it receives any integrated circuit chips. Such separate testing avoids expensive reworks and/or scrapping of the unit which the permanently joined chips and module form.
In the prior art, the probing of various contacts on the chips and the interconnect modules was performed by what is commonly called "a bed of nails". This bed of nails is comprised of a plurality of thin wires which are held in a cantilevered fashion such that their ends form a pattern which corresponds to the contacts that are to be probed. Thus the ends of the wires constitute probe tips. Electrical connections between these probe tips and the contacts on the chips or interconnect module are made by mechanically urging them together until the wires deflect slightly.
A problem, however, with these bed of nails probes is that the maximum density of the probe tips is too limited. State of the art probes can only be arranged in patterns of about 10 mils (254 micrometers) on center. By comparison, the transistors and their interconnect lines within an integrated circuit chip and interconnect module can have feature sizes of one micrometer or less.
Also, another problem with the bed of nails probes is that their wires are very fragile and are easily bent. Thus, as a practical matter, the total number of probes in a bed of nails is limited to less than 1,000. By comparison, the total number of contacts on a multichip interconnect module can be several thousand.
Still another problem with the bed of nails probe is that the force between a probe tip and its contact is determined by many factors which are difficult to control. For example, a probe wire may be slightly bent, or the contacts on an interconnect module may be at slightly different heights. And, an excessive probe tip force can damage the corresponding contact, whereas small probe tip force can yield an open circuit.
Accordingly, a primary object of the invention is to provide an improved electro-mechanical probe for testing microscopic circuits in which the above problems are overcome.